Hydraulic starting system having a source with a decaying pressure characteristic



Oct. 8, 1963 Filed Feb. 27. 1961 E. V. MANNING HYDRAULIC STARTING SYSTEM HAVING A SOURCE WITH A-DECAYING PRESSURE CHARACTERISTIC El AL 3,106,057

5 Sheets-Sheet 1 BY M-A/ ATTORNEYS 1 3,106,057 HYDRAULIC STARTING SYSTEM HAVING A SOURCE WITH A DECAYING 5 Sheets$heet 2 E. V. MANNING ET AL PRESSURE CHARACTERISTIC Oct. 8, 1963 Filed Feb. 27, 1961 mum INVENTORS' Eon flea M MANN/N6, Ja/Y/V BMW/VA;

ATTORNE5 1963 E. v. MANNING ET AL 3,

HYDRAULIC STARTING SYSTEM HAVING A SOURCE WITH A DECAYING PRESSURE CHARACTERISTIC Filed Feb. 2'7, 1961 5 Sheets-Sheet 5 w W J W MN m .I IIIWMIIIlIlWMIIIL INVENTORS EOIWPO KMfi/V/v/A/q Joly/V A NEW/wk;

ATTORNEYS 1963 E. v. MANNING ET AL 3,106,057

HYDRAULIC STARTING SYSTEM HAVING A SOURCE WITH A DECAYING' PRESSURE CHARACTERISTIC 5 Sheets-Sheet 4 Filed Feb. 27, 1961 em I.

INVENTORS Hit H190 1 MfiN/Vl/VG, Jay/v R mf/m/wv,

@Mfl M M ATTORNEYS 1963 E. v. MANNING ETAL 3,106,057

mmRAwuc swarms SYSTEM HAVING A SOURCE WITH A DECAYING' PRESSURE OHARACFIERISTIC Filed Feb. 27. .1961 s Sheets-Sheet 5 United States Patent 3,106,057 HYDRAULIC STARTING SYSTEM HAVING A SQURCE WITH A DECAYING PRESSURE CHARACTERISTIC Edward V. Manning, Watertown, and John P. Mentink, Rochester, N.Y., assignors to The New York Air Brake Company, a corporation of New .lersey Filed Feb. 27, 1961, Ser. No. 92,052 12 Claims. (Cl. 60-48) This invention relates to a starting system for internal combustion propulsion engines.

The use of hydraulic motors for starting internal combustion propulsion engines has been proposed in the past. Such hydraulic motors were driven by pressure fluid supplied by motor-driven auxiliary pumps and hence the starting systems were relatively complex and expensive.

The object of the present invention is to provide a hydraulic starting system which uses a variable displacement hydraulic unit driven as a motor by fluid supplied from a pressure fluid source, such as a pressure accumulator, having a decaying pressure characteristic. The starting system is characterized by the provision of pressure-responsive control means operable in dependency upon the decaying pressure of the fluid supplied by the source to maintain the hydraulic unit in a condition of maximum constant displacement and maximum torque until the internal combustion engine is started. By the use of such a source of decaying pressure fluid, the starting system may be designed to be completely self-contained in the vehicle and automatic control of the hydraulic unit is accomplished in a simple, positive manner.

According to the preferred embodiment of the invention, the hydraulic unit is of the motor-pump type and is designed to be driven as a variable-displacement pump by the internal combustion engine atte the latter obtains independent operation. By causing the hydraulic unit of the starting system to-operate as a pump subsequent to starting of the internal combustion engine, the need for auxiliary pumping apparatus for supplying pressure fluid to hydraulic loads of the vehicle is eliminated and the weight of the vehicle is reduced. The preferred embodiment of the invention also includes discharge pressure compensating means for regulating the displacement of the hydraulic unit during pumping operation to maintain discharge pressure constant at a given maximum value.

The hydraulic unit of the starting and pumping system comprises a device of the eve-reenter motor-pump type employing a rotary group of elements consisting of a cylinder barrel having longitudinal bores therein and reciprocatory pistons mounted in said bores, said rotary group being mounted for rotation with respect to an angularly adjustable cam plate suspended in the engine housing. As the rotary group of elements rotates relatively to the cam plate, reciprocatory motion is imparted to the pistons. The stroke of the pistons (and consequently the displacement of the hydraulic engine) is dependent upon the angle of inclination of the cam plate. The cam plate is movable between a maximum stroke-establishing (motoring) position on one side of a zero stroke-establishing (neutral) position and a maximum stroke-establishing (pumping) position on the other side of the neutral position.

During motoring operation of the hydraulic unit, the pressure-responsive control means operates to position the cam plate at the maximum stroke-establishing motoring position when the pressure of the accumulator fluid is above a predetermined value. When the pressure of the accumulator fluid gradualiy decreases to a predetermined value at start cut-out speed, the pressure-responsive control means displaces the cam plate to its zero strokeestablishing position. Since the hydraulic engine is al- "Ice Ways maintained at its constant displacement maximum stroke-establishing motoring condition as long as the pressure of the fluid from the accumulator is above the predetermined value, the maximum possible starting torque obtainable from the accumulator fluid will be applied to the internal combustion engine by the hydraulic unit throughout the entire starting period.

In order to cause the hydraulic unit to operate as a pump when the internal combustion engine achieves independent operation, speed-responsive control means are provided for moving the cam plate toward its maximum stroke-establishing pumping position when the speed of rotation of the internal combustion engine increases to a predetermined value. During the pumping operation of the hydraulic unit, the discharge pressure compensating means regulates the position of the cam plate between the maximum stroke-establishing pumping position and the zero stroke-establishing neutral position to maintain a constant discharge pressure.

The hydraulic unit thus operates as a constant displacement moto during the motoring operation and as a variable displ'acernent pump during the pumping operation.

The preferred embodiment of the invention will now be described in detail with reference to the accompanying drawings, in which:

FIG. 1 is an axial sectional view of the hydraulic unit showing the cam plate in its maximum stroke-establishing position on the pumping side of neutral.

FIG. 2 is a schematic diagram of the hydraulic starting and pumping system in the initial standby condition, the cam plate of the hydraulic unit being shown in its zero stroke-establishing neutral position.

FIG. 3 is a schematic diagram of the hydraulic system in the starting (i.e., motoring) condition, the cam plate being in its maximum stroke-establishing position on the motoring side of neutral.

FIG. 4 is a schematic diagram of the hydraulic system in the idling condition, the cam plate being at its zero stroke-establishing position.

FIG. 5 is a schematic diagram of the hydraulic system in its maximum displacement pumping condition, the cam plate being in the maximum stroke-establishing position corresponding to that illustrated in FIG. 1, and the control valve being illustrated diagrammatically.

Referring first to FIG. 1, the hydraulic unit 1 is of the overcenter type operable alternately as a motor and as a pump and includes a rotary group of elements consisting of 'a cylinder barrel having longitudinal bores therein and reciprocatory pistons mounted in said bores, said rotary group being mounted for rotation with respect to an angularly adjustable cam plate suspended in the housing of the unit. Such a hydraulic unit is disclosed in detail in the copending application of Tadeusz Budzich and Edward V. Manning Serial No. 789,996, filed January 29, 1959, and entitled, Overcenter Hydraulic Starter Pump.

The hydraulic unit comprises a housing 2 having a drive shaft 3 journalled therein to which is connected the rotary cylinder barrel 4. The rotary cylinder barrel 4 is in contiguous engagement at one end with the adjacent end face of stationary valve plate 5, which face contains arcuate high and low pressure ports in communication, respectively (through internal housing passages, not shown), with the housing high and low pressure ports 6, 7 (FIG. 2). These housing ports (not shown in FIG. 1) lie in the horizontal plane adjacent the right-hand portion of the housing on opposite sides of the axis of rotation of the drive shaft 3. As will be explained in greater detail below, during motoring operation of the hydraulic unit, pressure fluid is supplied from the source to housing high pressure port 6, and during pumping operation, the

hydraulic unit supplies pressure fluid from port 6.

The cylinder barrel 4 contains a circumferential series of through longitudinal cylinder bores 8 which are arranged to register sequentially with the arcuate ports in valve plate as the cylinder barrel rotates. Pistons 9, formed with spherical heads 10 for connection with sup porting shoes 11, are mounted in cylinder bores 8 for re iprocation by cam plate (control member) 13 and nutating plate 14. Nutating plate 14 is seated on a collar 15 secured to the drive shaft 3, said collar having a spherical outer surface which engages a similarly shaped recess formed in' the mutating plate.

The cam plate 13 is supported in housing 2 by cam plate yoke portions 16 and fixed housing-secured trunnions 17 (FIG. 2) for angular movement about a horizontal pivot axis extending in a direction normal to the axis of drive shaft 3. The angular position of cam plate 13 determines the length of the strokes of pistons 10, and the cam plate is free to move between maximum stroke-establishing motoring and pumping positions (FIGS. 3 and 5, respectively) on opposite sides of a zero stroke-establishing position (a vertical position as shown in FIGS. 2 and 4). A first positioning motor 2%) is arranged on one side of the cam plate pivot axis for pivoting the cam plate in the clockwise direction toward its maximum stroke-establishing motoring position, and a second positioning motor 23 is arranged on the other side of the cam plate pivot axis for pivoting the cam plate in the counterclockwise direction toward its maximum stroke-establishing pumping position. The first positioning motor 21) comprises a stationary cylinder 21 formed in the housing 2 and containing a slidable plunger 22, and the second positioning motor 23 comprises a stationary cylinder 24 containing a slidable plunger 25. Plungers 22 and 25 are connected at their free extremities to earn plate 13 by the articulated connecting rods as and 27, respectively. Coil compression springs 28 and 29, reacting between the plungers 22, 25, respectively, and their associated stationary cylinders, bias the plungers outwardly with respect to their cylinders to position the cam plate 13 in the Zero strokeestablishing position illustrated in FIG. -2 when the first and second positioning motors are de-energized. Each of the springs 23, 23 is slightly preloaded when the cam plate 13 is in the zero stroke-establishing position.

A hydraulic control motor 31), constituting part of a discharge pressure compensating circuit, which will be described in greater detail below, is provided for moving the cam plate 13 between its maximum stroke-establishing pumping position and its zero strokeestablishing position to vary the displacement of the hydraulic engine and thus maintain the pumped fluid pressure at a constant predetermined value. This control motor includes a stationary cylinder 31, formed as part of the housing 2, and a reciprocable plunger 32. The plunger 32 is provided with an axially extending portion 33 containing an axial recess 34. Connecting rod 35 is connected at one end to the cam plate 13 by the ball and socket connection 36, and, at the other end, is mounted for sliding movement in recess 34.

At one end the cylinder 31 is provided with an internal peripheral flange portion 31a which constitutes a stop for limiting outward travel of plunger 32. This flange portion 31a prevents the control motor 39 from moving the cam plate 13 in the clockwise direction beyond the zero stroke-establishing position. However, due to the free or lost motion connection defined by recess 34 and the connecting rod 35, the cam plate 13 may be moved in the clockwise direction beyond the Zero stroke-establishing position by other motive means (i.e., by the first positioning motor 29). Thus the control motor 30, when energized, controls the position of'cam plate 13 only when it is between its maximum stroke-establishing pumping position and its zero stroke-establishing position.

As illustrated diagrammatically by the dashed line 121 in FIG. 2, the drive shaft 3 of the hydraulic unit is mechanically connected to the power shaft '76 of the internal combustion engine '71. Referring to FIG. 1, it will be seen that this mechanical connection includes an intermediate shaft 122 journalled in the housing 2 and having at one end a splined coupling 12% Encircling the intermediate shaft 122 are two spur gears 123, 124 whose hubs 1253, 126 are journalled on their outer peripheries in an intermediatewall portion of the housing. Another hub portion 127 of gear 124 is journalled in a housing bore and supports the right end of intermediate shaft 122. These gears are connected with the intermediate shaft by one-way overrunning clutches 128, 129 and mesh with spur gears 131 and 132 which are formed in one piece with drive shaft 3. The cam elements 133 of clutches 128, 129 are set in reverse senses so that when the drive shaft 3 is driving the intermediate shaft 122, torque is transmitted through the gears 131 and 123, and when intermediate shaft 122 is driving shaft 3, torque is transmitted through gears 124 and 132. Both gear pairs 123, 133 and 124, 132 effect a step-down in speed, the pair 123, 131 having the higher ratio.

As shown in FIG. 2, an accumulator 39, containing hydraulic fiuid at a given initial pressure (for example, 3000 p.s.i.), is connected with the housing high pressure port 6 via the first conduit 4% which contains a starter valve 41 operable between closed and open positions. The housing low pressure port 7 is in continuous communication with sump d2. At a point intermediate valve 41 and high pressure port 6, the conduit 41} is joined by a conduit 43a leading to the inlet port 4-6 of first positioning valve which controls the state of energization of the second positioning motor 23. In addition to the inlet port 46, the 'valve 45 includes a pair of motor ports 4-8 and 49 which are connected with the working chamber 23a of the second positioning motor via branch conduits 44b, 44a, respectively, and the common conduit 440, an outlet port 4'7 which is connected with a second positioning valve '60 through conduit 43:2, and an exhaust port which is in continuous communication with sump 52. Reciprocable valve plunger 51, provided with annular lands SM, 510, 51c separated by annular grooves 51b, 51d, is mounted in a bore in the valve housing for controlling the communication between the various ports. Preloaded spring 52, arranged in one end of the valve housing bore, normally urges plunger 51 to the left against fixed stop 45a to a finst position illustrated in FIGS. 2, 4 and 5. When the plunger is in this first position, inlet port 46 communicates with first and third outlet ports 47, 49 through groove 51d, and second outlet port 4 8 is closed by land 510 to isolate exhaust port 5 3. The left-hand end portion of the plunger 51 (i.e., land 51a) cooperates with the contiguous bore wall portion to form valve motor 53 of the piston and cylinder type for moving the plunger to the right against the biasing force of spring 52 to a second position illustrated in FIG. 3. When the plunger 51 is in this second position, inlet port 46 remains in communication with first outlet port 47 via groove 51d, third outlet port 49 is closed byland 51c, and second outlet port 43 communicates with exhaust port 50 via groove 51b.

A second positioning valve 63 is provided for controlling the state of energization of the first positioning motor 211* as well as the operation of valve motor 53 and includes an inlet port 61 communicating with conduit 436, a pair of motor ports 62, -63 which are connected with working chamber 23a of the first positioning motor 211 via branch portions 43b, 43c, respectively, and common conduit 43d, and an exhaust port 64 which is in continuous communication with sump 4-2. A conduit 75 connects Working chamber 53a of' the valve motor 53 with the common conduit 43d through branch conduit 43b and thus valve motor 53 and positioning motor 23 are energized and die-energized simultaneously. Reciprocable plunger as, provided with annular lands 65a, 650, 65a separated by annular grooves 655, 65d, is mounted in a bore in the housing of the second positioning valve for controlling communication between the various valve ports. Preloaded spring 66, mounted in the right-hand end of the valve housing bore, normally urges plunger to the left to a first position shown in FIG. 2 in which inlet port 61 communicates with first outlet port 62 via groove 65d, and exhaust port 64 is closed by land 650. The plunger 65 is shiftable to the right to a second position shown in FIG. 5 by a centrifugal governor 67 driven by the internal combustion engine; in this second position, groove 65b connects ports 63 and 64 and land 65c closes ports 61 and 62.

Connected to housing high pressure port 6 via conduit 76b is the discharge pres-sure compensation control valve 77 which controls the operation of control motor 30 to maintain the discharge pressure developed at high pressure port 6 by the hydraulic engine 1 during pumping operation at a constant predetermined maximum value. The structure and operation of one embodiment of control valve 77 has been illustrated and described in detail in the Budzich et al. US. patent application Serial No. 789,996 filed January 29, 1959, referred to above. As shown diagrammatically in FIG. 5, the control valve comprises a housing having an inlet passage 7? connected with high pressure port 6 via conduit 7612, a motor passage 81 connected with working chamber 36a of control motor 30 via conduit 76a, and an exhaust passage 82 connected with sump 42 via conduit 83. The valve housing is formed with a longitudinal bore 84 in which is mounted at one end a first slidable valve plunger 85 and at the other end a slidable spring seat 86. The valve plunger 85 carries annular lands 87, 88 and S? which are separated by annular grooves 91 and 92. The annular land 87 contains longitudinal slots 93, and the spring chamber 94 intermediate the spring seat 86 and the valve plunger 85 is in continuous communication with motor passage 8d via longitudinal and radial passages 95- and 96, respectively, in the plunger 55. Spring 97, reacting between seat 36 and valve plunger 65, biases the plunger to the left into contact with the end wall of the valve housing.

The control valve 77 also includes a second slidable valve plunger 101 mounted in housing longitudinal bore 102. The valve plunge-r 101 is provided with annular lands 103, 104 and 105 separated by annular grooves 166 and 107. The housing is provided with exhaust passage 108 connected with sump 42, outlet passage 109 communicating with the working chamber behind spring seat '86 via passage 111, and inlet passage .112. connected with conduit 76a via passage 113. A stationary solenoid 114, having a movable armature 115 which is connected with plunger 3101, serves, when energized, to shift the plunger 101 to the left against the biasing force of spring 116.

As will be more fully explained below, the solenoid 114 controls the operation of control valve 77 (by controlling the effective loading of spring 97) to selectively establish one of two different reference pressure values against which the pressure of fluid at the housing high pressure port 6 is compared. When the pressure of the fluid at high pressure port 6 is below a selected one of the two reference pressure values established by control valve 77, the control valve 77 serves to interrupt communication between conduits 76a and 76b and to connect conduit 76:: with sump conduit 83, whereby working chamber 30a is vented and control motor Sit is deenergized. When the pressure of the fluid at the housing high pressure port 6 exceeds the predetermined reference pressure established by the control valve 77, the conduits 76a, 76b are brought into communication, the exhaust conduit 83 is closed, and fluid having a pressure equal to the difference between the pressure of the fluid at the housing high pressure port 6 and the reference pressure is applied to the worxing chamber 30a of con trol motor 30 to vary the position of cam plate 13 between its maximum stroke-establishing pumping position and its zero stroke-establishing neutral position.

When the lower of the two reference pressure values is established by control valve '77 (as determined by the state or" energization of solenoid 114), the maximum discharge pressure at housing high pressure port 6 will be automaticaly maintained constant at a lower value (3000 p.s.i. for normal starting and operating conditions, for example), and when the higher of the two reference pressures is selected by the solenoid control mechanism 114, the maximum discharge pressure at port 6 will be automatically maintained constant at a higher value (4000 p.s.i. for starting of the internal combustion engine at extremely low temperatures, for example). In either event, the discharge pressure compensating circuit serves to apply to the working chamber 30a of the control motor 36 fluid having a pressure equal to the amount by which the pressure at the housing high pressure port 6 exceeds the selected one of the two reference pressures.

T e conduit 40 is connected with the hydraulic system of the vehicle via system conduit 156 containing shutoff valve 151 operable between closed and open positions.

OPERATION The operation of the hydraulic starting and pumping system may now be described.

(1) Motoring Operation for Starting the Internal Combustion Engine that the accumulator 39 contains fluid at an initial pressure of 3000 p.s.i., as soon as the starter valve 41 is opened, pressure fluid from accumulator 39 flows to the housing high pressure port 6 through conduit 40. Fluid also flows through conduit 43a, valve 45, conduit 432, and conduits 43b and 43d to the working chamber 20a of the positioning motor 26, and from conduit 43b to working chamber 53a of valve motor 53 via conduit 75. The pressure in working chamber 53a rises immediately to 3000 p.s.i. and causes valve motor 53' to shift plunger 51 to the right to its second position (FIG. 3) to vent Working chamber 23a to sump through common conduit 44c, branch conduit 44b, motor port 48, groove 51b, and exhaust port 50. Since positioning motors 20 and 23 are now pressurized and vented, respectively, cam plate 13 is shifted to the maximum stroke-establishing motoring position of PEG. 3, increasing the compression of spring 29 and decreasing the compression of spring 28. The accumulator pressure fluid applied to high pressure port 6 is conducted through internal passages (not shown) to the high pressure arcuate port in the end face of valve plate 5 to move the pistons 9 in their respective cylinder barrel bores, and the pistons react with the inclined cam plate 13 to develop torque on the cylinder barrel to effect motoring operation of the hydraulic engine. Since the cam plate 13 is constantly maintained in its maximum strokees-tablis'ning motoring position as long as the accumulator fluid pressure is above a predetermined value (namely that pressure at which motor 53 holds plunger 51 in the FIG. 3 position), the hydraulic unit operates as a constant maximum-displ-acement motor throughout the starting cycle to apply the maximum possible starting torque obtainable from the accumulator pressure fluid to the internal cornbustion engine via mechanical connection 121.

(2) Idling Operation of the Hydraulic Engine Due to the pressure fluid demand on the accumulator 39 caused by the hydraulic unit 1 during its motoring operation, the accumulator fluid pressure progressively decreases in accordance with its inherent accumulator decay characteristic until at starter cutaout speed (is, the speed of operation of the hydraulic engine at-which the internal cacao-e7 combustion engine is assumed to have started and to have reached independent operation) the accumulator pressure reaches the predetermined value (1500 p.s.i., for example). In accordance with the engineering design of the system, when the pressure in v/orl'ing chamber 53a (transmitted from conduit 40 via conduit 43a, groove 51a, conduit 43c, groove 65d, and conduit 75) decreases to this value, the biasing force of spring 52 is no longer overcome and the movable valve member 1 is displaced to the left by the spring 52 to its first position (as shown in FIG. 4) whereby exhaust port 5% is closed and fluid under the reduced pressure of 1500 psi. is applied to the working chamber 2.3a. Since the pressure of working chamber 201: has meanwhile decreased to 1500 p.s.i., both positioning motors and 23 are equally pressurized and springs 23 and 29 react to position the cam plate 13 at its zero strokeestablishing position as shown in 1 1G. 4. The hydraulic unit now operates at its idling condition and the internal combustion engine operates independently of the hydraulic starting system.

(3) Pumping Operation of the Hydraulic Engine After the internal combustion engine 71 has been started by the hydraulic unit 1 as outlined above, the speed of rotation of the engine shaft 70 gradually in creases from starter cut-out speed to a predetermined operating speed at which the internal combustion engine develops suflicient power to drive the hydraulic unit as a pump. When the speed of rotation of shaft 70 reaches this predetermined operating speed as sensed by the centrifugal governor 67 connected thereto by the mechanical connection 72, the centrifugal governor operates to shift the movable valve member 65 to the right against the biasing action of spring as to the second position illustrated in FIG. 5 to de-energize the first positioning motor 2t by connecting the working chamber Zila thereof to sump 42.

Since the conduit 75 is now connected with the sump 42, the movable valve member 51 of the first positioning valve 45 remains at its left-hand first position due'to the biasing action of spring 52. The working chamber 23a of the second positioning motor 23 continues to be supplied with accumulator fluid at the reduced pressure of 1500 p.s.i. through conduit 43a, groove Sid, and conduits @411, 44c, and since the Working chamber 20a of the first positioning motor 20 is tie-energized by valve es in its second position, the cam plate 13 is moved overcenter by the second positioning motor 23 to the maximum strokee-stablishi-ng pumping position illustrated in FIG. 5.

The drive shaft 3 and the rotary cylinder barrel 4 are driven by the shaft 70 of the internal combustion engine through the mechanical connection 121 and, since cam plate 13 is in its maximum stroke-establishing pumping position, the pistons 9 are reciprocated as the cylinder barrel rotates and the hydnaulic engine operates as a pump delivering fluid from the high pressure port 6. The acclnnul-ator is recharged by the pump and is available for other system functions, and high pressure fluid is now available for delivery to auxiliary hydraulic loads through system conduit 150 upon the opening of shut-oil valve 151.

During pumping operation, the hydraulic unit 1 operates as a variable displacement pump under control of the discharge pressure compensating means referred to above. Assuming that the cam plate 13 is in the maximum strokeestablishing pumping position and the solenoid 114 is in the de-ener-gized state as shown in FIG. 5, pressure fluid from the housing high pressure port 6 is conducted through conduit 76b to the inlet passage '79 of the discharge pressure compensation control valve 77. The working chamber 30a. of control motor 30 is connected to sump 42 through conduit 76a, motor passage 81, groove 92, exhaust passage 82, and conduit 83, and the spring chamber $4 is connected to sump through lon gitudinal and radial passages 95, 96, motor passage 81,

groove 92, exhaust passage 82, and conduit 33. As the pressure of the pumped fluid builds up at the housing high pressure port 6, the pressure increase is transmitted to inlet passage 79 via conduit 76b and is applied to the lcft hand portions of lands 87 and 83, whereby valve plunger is moved to the right against the biasing action of spring @7 to a lap position at which land 88 internupts communication between motor passage $1 and exhaust passage 32 to discontinue venting to sump of the working chamber 3th: and spring chamber 9d. The pressure required to hold valve plunger 85 in this lap position against the biasing force of spring 97 is the reference pressure against which the fluid pressure at high pressure port 6 is compared. Assuming that it is desired to maintain the discharge pressure at port 6 constant at a maximum value of 3000 p.s.i. and that the elements of control valve 77 are so dimensioned as to establish a first reference pressure of 1500 p.s.i., then, when discharge pressure exceeds 1500 p.s.i. valve plunger 85 moves further to the right to thereby interconnect inlet passage 79 with motor passage 81 through slots 93 and groove 91. Pressure fluid is now transmitted to working chamber 3% through conduit 76a and to spring chamber 94 through radial and longitudinal passages 06 and 95. When the pressure in these two chambers rises to a value at which the sum of the force of spring g7 and the pressure force acting on the right end of valve plungor 35 exceeds the pressure force acting on the left end of this plunger, the valve plunger 85 moves to the left toward its lap position. When it has again reached the lap position, the pressures established in Working chamber 3 2a and spring chamber 94 will be equal to the difference between discharge pressure in conduit 76b and the reference pressure. Further increases in discharge pressure produce equal increases in pressure in working chamber 30a and spring chamber 94.

The pressure in working chamber 30a, acting on control piston 32, urges the cam plate 13 toward its zero stroke-establishing position against the opposing resultant force of positioning motor 23 and spring 29. The parts are so dimensioned that when the discharge pressure in conduit 76!) reaches the 3000 p.s.i. maximum value, the cam plate 13 will be in its zero stroke-establishing position.

During the operation of control valve 77 described above for maintaining discharge pressure constant at the 3000 p.s.i. maximum value, solenoid 114 is in the de-cnergized state to establish a reference pressure of 1500 p.s.i. and spring seat 86 is in contact with the housing projection 84a. The portion of longitudinal bore 84 to the right of spring seat as is connected with sump through conduit ill, outlet passage 109, groove 1%, and exhaust passage ltlbj When the solenoid 114 is energized, the preloading on spring $7 is increased to establish a second reference pressure of 2000 p.s.i. in order to maintain the discharge pressure at a maximum value of 4000 p.s.i. for pumping operation at lower temperature conditions. This is accomplished as follows. When valve plunger 101 is moved to the left by solenoid 114 against the biasing action of spring 116, land 1 04 closes exhaust passage 103 and conduit 113 is brought into communication with conduit 111 through inlet passage 112, groove 107, and outlet passage 109. Fluid from high pressure port 6 is applied to the right-hand side of spring seat 86 and moves the same to the left against fixed stop 84?) to increase the pre loading of spring 97 whereby the second reference pressure of 2000 p.s.i. is established. The control valve 77 and control motor 30 then operate in the manner described above to maintain the discharge pressure at the 4000 p.s.i. maximum value, and when this discharge pressure is obtained, cam plate 113 is positioned by control motor 30 at the zero stroke-establishing position.

As mentioned above, due to the stop flange 31a and to the lost motion connection between recess 34 and connecting rod 35, the control motor 30 controls the position of cam plate 13 only when the cam plate is between its maximum stroke-establishing pumping position and its zero stroke-establishing neutral position, and hence detailed description of the operation of the discharge pressure compensating means during motoring operation of the hydraulic engine is not necessary. With reference to the energization of motor 30 in FIG. 2, it is obvious from the above description that when the accumulator pressure at high pressure port 6 exceeds the reference pressure established by valve 77, plunger 85 is shifted to the right beyond its lap position to interconnect conduits 76b and 76a (via slots 93 and groove 71) whereby chamber 30:: is pressurized and piston 32 is shifted to its illustrated right-hand end position. The piston will remain in this position (FIGS. 3 and 4-) until it is shifted to the left by rod 35 when motor 30 is vented and cam plate 13 is pivoted to the pumping side of neutral (FIG. 5).

The use of the overcenter type of hydraulic unit described above in the hydraulic starter system presents the advantage that only one high pressure line is required since the high pressure inlet line during motoring operation becomes the high pressure discharge line during pumping operation without changing the direction of rotation of the drive shaft 3 and the rotary cylinder barrel 4. The self-contained hydraulic system using an accumulator as the prime source of hydraulic energy presents a very simple and durable internal combustion engine starting device providing high power-to-weight ratios for various operating conditions. By providing the accumulator with a hand pump or other charging device, the system is capable of making initial starts on newly serviced systerns without requiring external supporting equipment.

Although the invention has been illustrated and described as using a centrifugal governor 67 for operating the second positioning valve 60 to achieve the transition to pumping operation, it is obvious that other types of motive means operated either manually or by an external or internal control signal may be utilized equally as well.

While in accordance with the provisions of the patent statutes we have illustrated and described the best form and embodiment of the invention now known to us, it will be apparent to those skilled in the art that other changes may be made in the apparatus described without deviating from the invention set forth in the following claims.

What is claimed is: 1

l. A hydraulic system comprising a hydraulic unit having high and low pressure ports and a displacement control element movable between minimum and first maximum displacement-establishing positions; a source of pressure fluid having a decaying pressure characteristic; a conduit connecting the source with the high pressure port; and'means associated with the displacement control element and responsive to the pressure in the conduit for positioning said element in its first maximum displacement-establishing position when the pressure is above a predetermined value and for positioning said element in its minimum displacement-establishing position when the pressure is below that value.

2. Apparatus as defined in claim 1 wherein said control element positioning means includes spring means biasing said control element toward its minimum displacement-establishing position, a pair of opposed positioning motors connected with said control element, and pressureresponsive means for energizing one of said positioning motors and for de-energizing the other of said positioning motors when the pressure in said conduit is above said predetermined value to position said control element in its first maximum displacement-establishing position.

3. Apparatus as defined in claim 1 wherein said source of pressure fluid is an accumulator.

4. Apparatus as defined in claim 1 wherein said hydraulic unit is of the overcenter type, and further including means for positioning said control element in a second maximum displacement-establishing position on the opposite side of said minimum displacement-establishing position from said first maximum displacement-establishing position.

5. A hydraulic motoring and pumping system comprising a variable displacement hydraulic unit of the longitudinally reciprocating-piston rotary cylinder barrel type operable alternately either as a motor or as a pump, said unit having high and low pressure ports and a pistonstroke control element movable between first and second maximum stroke-establishing positions on opposite sides of a zero stroke-establishing position; a source of pressure fluid having a decaying pressure characteristic; 2. first conduit connecting the source with the high pressure port; first spring means biasing said control element toward its zero stroke-establishing position; first and second opposed positioning motors connected with said control element for positioning said element in its first maximum stroke-establishing position when said first positioning motor is energized and said second positioning motor is de-energized and for positioning said element in its second maximum stroke-establishing position when said first positioning motor is de-energized and said second positioning motor is energized, said control element being positioned in its zero stroke-establishing position by said first spring means when both of said positioning motors are energized; a second conduit connecting said first positioning motor with said first conduit; a third conduit connecting said second positioning motor with said first conduit; a first positioning valve connected in said third conduit and including an exhaust passage, a valve member movable between first and second positions in which, respectively, it connects said second positioning motor with said first conduit and with said exhaust passage, and second spring means biasing said movable member toward its first position; a second positioning valve in said second conduit, said second positioning valve having an exhaust passage and a valve member movable between first and second positions in which, respectively, it connects said first positioning motor with said first conduit and with said exhaust passage; pressure-responsive means connected with the movable member of said first positioning valve for moving it to its second position; means, including the second positioning valve, for connecting the pressure-responsive means with the first conduit when said second positioning valve is in its first position, and, when that valve is in its second position, for venting the pressure-responsive means; and means for shifting the movable member of said second positioning valve to its second position.

6. Apparatus as defined in claim 5 wherein said unit includes a [rotary output shaft and further wherein said means for placing the movable valve member of said second positioning valve in its second position comprises a speed-responsive device operable as a function of the speed of rotation of said output shaft.

7. Apparatus as defined in claim 5 and further including discharge pressure compensating means operable as a function of the fluid pressure at the high pressure port for moving said control member between its second maximum and zero stroke-establishing positions to maintain the pressure of the fluid at said high pressure port at a constant predetermined maximum value.

8. Apparatus as defined in claim 7 wherein said discharge pressure compensating means includes a hyl 1 sure port and said reference value when the high pressure port pressure exceeds said reference value.

9. Apparatus as defined in claim 8 wherein said control motor includes a movable element, and wherein said discharge pressure compensating means further includes stop means preventing said control motor movable element from moving said control element beyond its zero strokeestablishing position toward its first maximum strokeestablishing position, and a lost-motion connection connecting said control motor movable element with said control member and permitting free movement of said control element toward its first maximum stroke-establishing position independently of said control motor.

10. Apparatus as defined in claim 8 and further wherein said control valve includes auxiliary valve means operable to establish a second reference pressure value which is greater than the first reference pressure value.

11. The method of accelerating an engine to starter cut-out speed during a starting cycle using a variable displacement motor comprising supplying fluid to the motor at a pressure that decreases as the time of operation of the motor increases; operating the motor at maximum displacement from the beginning of the starting cycle until supply pressure reduces to a predetermined value; and thereafter reducing motor displacement toward zer 12. The method defined in claim 11 in which said predetermined value is selected to indicate that the engine has reached cut-out speed; and in which motor displacement is reduced rapidly toward zero when supply pressure reaches said predetermined value.

References Cited in the file of this patent UNITED STATES PATENTS 2,171,257 Nar done Aug. 29, 1939 2,838,908 Forster June 17, 1958 2,945,449 Le Febvre et al July 19, 1960 2,986,872 Budzich June 6, 1961 

11. THE METHOD OF ACCELERATING AN ENGINE TO STARTER CUT-OUT SPEED DURING A STARTING CYCLE USING A VARIABLE DISPLACEMENT MOTOR COMPRISING SUPPLYING FLUID TO THE MOTOR AT A PRESSURE THAT DECREASES AS THE TIME OF OPERATION OF THE MOTOR INCREASES; OPERATING THE MOTOR AT MAXIMUM DISPLACEMENT FROM THE BEGINNING OF THE STARTING CYCLE UNTIL SUPPLY PRESSURE REDUCES TO A PREDETERMINED VALUE; AND THEREAFTER REDUCING MOTOR DISPLACEMENT TOWARD ZERO. 